1. Field of the Invention
The present invention is related to a limiting circuit for a brushless dc motor. More particularly, the present invention is related to a simplified limiting circuit for a brushless dc motor.
2. Description of the Related Art
A motor speed will be gradually reduced due to covering it with dust. Accordingly, an electric current passing through a motor coil is rapidly risen and the power consumption is thus increased. Also, as a fan wheel is jammed, an electric current passing through the motor coil is rapidly risen and the power consumption is thus increased. Great power consumption can generate high temperature and heat that may result in cracks in an insulating material of wire of the motor coil.
In order to prevent from passing of a greater electric current through the motor coil during abnormal operation, there is an auto restart function build in a drive IC. When the motor is operated abnormally, a series of pulsed signals are used to allow a current to pass through the motor coil a short-term time, such as a few seconds, and thus a successive passage of a greater electric current is prevented. After passing an electric current for a short term, the electric current on the motor coil is interrupted if an abnormal operation of the motor coil is not removed. And the drive IC produces a series of pulsed signals to restart the motor coil shortly after the interruption of the electric current on the motor coil. The auto restart function may be operated repeatedly as long as the abnormal operation of the motor coil remains. However, the auto restart function may still allow a pulsed electric current through the motor coil to thereby consume its maximum power when the motor is restarted.
Briefly, there is a need for an effective limit which can avoid great power consumption and high temperature when the motor speed is reduced or the fan wheel is jammed.
The present invention intends to provide a limiting circuit for a brushless dc motor, which includes a simplified limiting circuit connected to a motor drive circuit to thereby limit an electric current supplied from a power source in such a way to mitigate and overcome the above problem.